1. Field of the Invention
This invention relates to a radial tire for heavy load vehicles such as trucks, buses or the like, which is constructed to effectively suppress a wandering phenomenon of the tire.
2. Description of the Prior Art
In the specification, the wandering phenomenon shall be understood to mean a phenomenon experienced often by a driver of a heavy load vehicle such as a large type truck or the like when it runs in a wheel track formed when a highly used paved road surface becomes depressed or worn due to the vehicle weight, particularly when a driver tends to change the direction of the vehicle or to get away the vehicle from the wheel track in order to avoid an obstacle scattered thereon.
The radial tire for trucks and buses has a boundary between a tread and a sidewall provided with a sharp edged square shoulder has particularly been subjected to the wandering phenomenon. As a result, it has heretofore been proposed to use a round edged round shoulder tire for the purpose of alleviating the resistance to shocks subjected to the shoulder edge when the tire rides across the wheel track and hence of suppressing the wandering phenomenon.
Such a round shoulder configuration is affected by the bending of the tire produced by the dynamic load due to the amount of load or the vibration when the vehicle not only runs around the corner but also runs straight ahead. As a result, the round shoulder functions as a partial ground contact region. That is, this partial ground contact region is a rounded portion and hence is subjected to a ground contact pressure which is lower than that subjected to a relatively flat tread. The round shoulder therefore tends to easily respond to the local step or movement which is liable to be occur between the round shoulder and the ground surface in the ground contact region, thereby inducing an abnormal premature wear, that is, a shoulder wear.